Method and installation for energy production by means of a gas turbine associated with an air separation unit

ABSTRACT

A method which include an air intake into an air separation unit; extracting from the separation unit at least a gas stream, essentially consisting of an air gas, in particular oxygen or nitrogen, and directing one or more of these gas streams towards the combustion chamber of a gas turbine; controlling at least one parameter related to the or each gas stream, by acting on a compressor in each gas stream arranged downstream of the air separating unit; assigning to one or more parameter a variable setpoint value, based on a value representing the load of the gas turbine.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and to an installation forproducing energy by means of a gas turbine associated with an airseparation unit.

2. Related Art

In a conventional way, a gas turbine comprises a compressor, acombustion chamber, and an expansion turbine, coupled to the compressorto drive the latter. This combustion chamber receives a combustion gas,together with a certain amount of nitrogen whose purpose is to lower theflame temperature in this combustion chamber to make it possible tominimize the emissions of nitrogen oxides to the atmosphere.

In a known way, the combustion gas can be obtained by gasification,namely by oxidation of carbon-containing products, such as coal oralternatively residues from the petroleum industry. This oxidation isperformed in an independent unit known as a gasifier.

In a conventional way, it is possible to associate this gas turbine withan air separation unit. The latter, which is usually a cryogenic unitcomprising at least one distillation column, is able to supply, fromair, at least one gaseous stream consisting predominantly of one of thegases in the air, particularly oxygen or nitrogen.

Combining this air separation unit with the gas turbine consists inmaking good use of at least one of the two aforesaid gaseous streams.For this, the oxygen and nitrogen produced in the air separation unitare admitted into the gasifier and into the combustion chamberrespectively.

U.S. Pat. No. 5,501,078 and EP-A-0 773 416 describe methods in which thepressures of the gases compressed by the oxygen and nitrogen compressorsare constant.

U.S. Pat. No. 5,802,875 has no means for acting directly on the nitrogencompressor but a valve downstream thereof which acts indirectly on thecompressor to alter the nitrogen flow rate.

SUMMARY OF THE INVENTION

The invention proposes to employ a method of this type, in a way that isparticularly economical, particularly in terms of power requirement.

To this end, its subject is a method for producing energy using a gasturbine associated with an air separation unit, in which method air isadmitted into said separation unit, at least one gaseous streamessentially consisting of a gas from the air, which is of oxygen or ofnitrogen is extracted from said separation unit, and the gaseous streamis directed toward a combustion chamber of the gas turbine, in the caseof nitrogen, or toward a gasifier in the case of oxygen, characterizedin that at least one parameter associated with the or each gaseousstream is controlled by direct action on a compressor for this gaseousstream which is located downstream of said air separation unit, and inthat a variable setpoint value that varies as a function of a valuerepresentative of the load on the gas turbine is assigned to the or eachparameter.

BRIEF DESCRIPTION OF THE DRAWINGS

For a further understanding of the nature and objects for the presentinvention, reference should be made to the following detaileddescription, taken in conjunction with the accompanying drawings, inwhich like elements are given the same or analogous reference numbersand wherein:

FIG. 1 illustrates a first embodiment of the invention; and

FIG. 2 illustrates a second embodiment of the invention.

The compressor can be acted upon directly by altering the compressorvanes or by altering the speed of the turbine driving it.

DESCRIPTION OF PREFERRED EMBODIMENTS

According to other features of the invention:

-   -   the parameter associated with said or with at least one of said        gaseous streams is the flow rate;    -   the gaseous stream is essentially formed of oxygen, this oxygen        is admitted into a gasifier that also receives carbon-containing        products, and the value representative of the load on the        turbine is the flow rate of carbon-containing products admitted        into the gasifier;    -   the gaseous stream is essentially formed of nitrogen, this        stream is admitted into the combustion chamber, and the value        representative of the load on the turbine is the flow rate of        fuel gas admitted into this combustion chamber: as a preference,        there is no regulating valve between the compressor and the        combustion chamber;    -   no control of the nitrogen pressure is exerted at the        compressor;    -   the parameter associated with said or with at least one of said        gaseous streams is the pressure;    -   the value representative of the load on the turbine is a        specific pressure value on the intake side of the gas turbine,        particularly in a delivery circuit running between a compressor        coupled to said turbine and the combustion chamber;    -   the gaseous stream is essentially formed by nitrogen and a first        setpoint value equal to said particular pressure increased by a        first safety value is assigned to the pressure of this stream;    -   the first safety value is between 0.1 and 10 bar, particularly        between 0.3 and 2 bar;    -   the gaseous stream is essentially formed of oxygen, and a second        setpoint value equal to said particular pressure increased by a        second safety value is assigned to the oxygen pressure;    -   the second safety value is between 2 and 20 bar, particularly        between 3 and 10 bar;    -   the pressure inside a gasifier feeding the combustion chamber        with fuel gas is also controlled by assigning to it a variable        setpoint point that varies as a function of said particular        pressure value;    -   the setpoint value is equal to said particular pressure, to        which a third safety value is added;    -   the third safety value is between 0.5 and 10 bar, particularly        between 1 and 5 bar.

Another subject of the invention is an installation for producing energyby means of a gas turbine associated with an air separation unit, thisinstallation comprising means allowing at least one gaseous streamessentially consisting of a gas from the air, which is of oxygen or ofnitrogen to be extracted from the separation unit, and means forconveying the gaseous stream toward a combustion chamber of the gasturbine in the case of nitrogen or toward a gasifier in the case ofoxygen, characterized in that control means are provided for controllingat least one parameter associated with the or with each gaseous stream,these means being able to act directly on a compressor for this gaseousstream, said control means having a variable setpoint value that variesas a function of a value representative of the load on the gas turbine.

According to other features of the invention:

-   -   the control means are means for controlling the flow rate;    -   the control means are able to control the flow rate of oxygen        flowing along a line emerging into a gasifier intended to feed        the combustion chamber, this gasifier also being placed in        communication with a line for conveying carbon-containing        products, and means are provided for controlling the flow rate        of the carbon-containing products admitted to the gasifier,        these means being able to control the means for controlling the        oxygen flow rate;    -   the control means are able to control the flow rate of a stream        of nitrogen flowing along a pipe opening into the combustion        chamber, also placed in communication with a pipe for conveying        fuel gas, and means are provided for controlling the flow rate        of fuel gas, these means being able to control the means for        controlling the flow rate of the stream of nitrogen;    -   the control means are means for controlling the pressure of said        or at least one of said gaseous streams;    -   measurement means are provided for measuring a particular        pressure value on the inlet side of the gas turbine,        particularly in a delivery circuit running between a compressor        coupled to the turbine and the combustion chamber, and operating        means are also provided so that the means for controlling the        pressure can be slaved to said measurement means;    -   means are also provided for controlling the pressure of the        gasifier, together with operating means allowing these control        means to be slaved to the measurement means.

The invention will be described hereinafter with reference to theattached drawings which are given solely by way of nonlimiting examples,in which FIGS. 1 and 2 are schematic views illustrating installationsaccording to two embodiments of the invention.

In these figures, lines drawn in bold are for conveying fluids, whereaslines drawn in dotted line are control lines.

The installation depicted in FIG. 1 comprises a gas turbine, denotedoverall by the reference 2 and which comprises, in the conventional way,an air compressor 4, an expansion turbine 6 coupled to the compressor 4,and a combustion chamber 8.

This gas turbine 2 is also provided with an alternator 10, driven by ashaft 12 common to the compressor 4 and to the turbine 6. A device formeasuring the load on the gas turbine, that is to say for measuring thedemand for power associated with it, is illustrated by a box 14, placednear the alternator 10.

The installation of FIG. 1 also comprises an air separation unit denotedoverall by the reference 16. The latter, which is of known type, issupplied with air by a pipe 18. It operates cryogenically, and for thispurpose has several distillation columns, not depicted.

A line 20 is able to remove, from the unit 16, a first stream W ofresidual nitrogen (nitrogen containing a few % of oxygen). This line 20opens into a compressor 22 downstream of which there is a pipe 24opening into the combustion chamber 8.

Furthermore, a line 26 is able to remove, from the unit 16, anoxygen-rich gaseous stream GOX. This line 26 opens into a compressor 28downstream of which there is a pipe 30. The latter opens into a gasifier32, of conventional type, which is also supplied, via a line 34 equippedwith a regulating valve 35, by a reservoir 36 containingcarbon-containing products, such as coal.

A pipe 38, which runs downstream of the gasifier 32, conveys the fuelgas resulting from the oxidation of the aforesaid carbon-containingproducts. This pipe 38 is placed in communication with the combustionchamber 8 of the gas turbine.

The device 14 for measuring the load is connected to the valve 35, by acommand line 40. What this means, in other terms, is that an increase inthe load 14 entails an increase in the flow rate of carbon-containingproducts conveyed in the line 34. Furthermore, the latter is providedwith a device 42 for controlling the flow rate, which is placed incommunication, via a command line 44, with a device 46 for controllingthe oxygen flow rate in the pipe 30.

Finally, the pipe 38 is equipped with a device 48 for controlling theflow rate of the fuel gas flowing therein. The device 48 is placed incommunication, via a command line 50, with a device 52 for controllingthe flow rate of residual nitrogen flowing in the pipe 24.

The overall operation of the installation of FIG. 1 will now bedescribed.

A certain flow rate of carbon-containing products is admitted to thegasifier 32 via the line 34 as a function of the load on the gasturbine. Oxygen is also admitted to the gasifier, so as to produce afuel gas, delivered by the pipe 38. There is a predetermined combustionratio R1 between the respective flow rates of carbon-containing productsand oxygen.

The fuel gas conveyed by the pipe 38 opens into the combustion chamber 8of the gas turbine. This combustion chamber also receives residualnitrogen, from the pipe 24. The dilution ratio corresponding to theratio between the flow rates of fuel gas and of residual nitrogen istermed R2.

The combustion chamber 8 also receives, via a pipe 53, compressed airfrom the compressor 4. The gases resulting from the correspondingcombustion, mixed with residual nitrogen, are sent to the inlet side ofthe expansion turbine 6, where they expand, driving this turbine. Thisalso, via the shaft 12, drives the compressor 4 and the alternator 10which powers, for example, an electricity distribution network, notdepicted.

When the load on the gas turbine 2 varies, this causes a correspondingvariation in the flow rate of carbon-containing products flowing alongthe line 34. This flow rate is controlled via the device 42 which then,via the line 44, sends a command to the control device 46, so that theflow rate of oxygen in the pipe 30 is adjusted accordingly, so that thecombustion ratio R1 is maintained.

The device 46 for controlling the flow rate acts directly on thecompressor 28 in a way known per se, for example on the vanes thereof.It should be noted that no pressure control is performed on the outletside of this compressor 28. Furthermore, there is no valve needed on thepipe 30.

Thus, the pressure of oxygen flowing through the pipe 30 becomesestablished spontaneously, as a function in particular of thecharacteristic of the gas turbine, and that of the compressor 28.

The flow rate of oxygen flowing through the pipe 30 is thereforeassigned a variable setpoint value that varies as a function of the flowrate of carbon-containing products conveyed by the line 34, the latterflow rate being itself commanded via the load on the turbine andtherefore representative of this load.

Furthermore, when there is such a variation in load, the flow rate offuel gas flowing in the pipe 38 varies accordingly, because of thevariations in the flow rates of the carbon-containing products andoxygen. The flow rate of the fuel gas is controlled via the device 48which then sends, via the line 50, a command to the device 52 so thatthe latter controls the flow rate of residual nitrogen flowing along theline 24 so that the ratio R2 is maintained. The control device 52 actsdirectly on the compressor 22, in a way similar to that which wasdescribed regarding the device 46 and the compressor 28.

As in the case of the compressor 28, it should be noted that no controlof the residual nitrogen pressure is implemented at the compressor 22.This pressure is therefore established spontaneously, particularly as afunction of the characteristics of the gas turbine and of the compressor22. Furthermore, no valve is needed on the line 24.

The flow rate of residual nitrogen flowing through the line 24 istherefore assigned a variable setpoint value that varies as a functionof the flow rate of fuel gas, the latter flow rate being itselfrepresentative of the load on the turbine.

FIG. 2 illustrates an alternative form of embodiment of the invention.

This alternative form of embodiment differs from the installation ofFIG. 1 in that the control device 46′, similar to the one 46, acts noton the compressor 28 but on an injection valve 54 placed on the pipe 30.Furthermore, this pipe 30 is equipped with a device 56 acting on thecompressor 28 with a view to controlling the oxygen pressure.

The installation of FIG. 2 also differs from that of figure 1 in thatthe device 52′for controlling the flow rate, similar to the one 52, actsnot on the compressor 22 but on a valve 58 placed on the pipe 24. Thispipe 24 is also equipped with a device 60 for controlling the residualnitrogen pressure, acting directly on the compressor 22.

The installation of FIG. 2 finally differs from that of FIG. 1 in thatthe gasifler 32 is provided with a device 62 for controlling thepressure inside this gasifier. This device 62 acts on a valve 64, withwhich the fuel gas pipe 38 is equipped.

The setpoints assigned to the various control devices 56, 60 and 62 havea variable value that varies as a function of the load on the gasturbine.

For this purpose a sensor 66 is used to measure the pressure in the airdelivery circuit, which places the compressor 4 in communication withthe combustion chamber 8. The setpoint values of the devices 56, 60 and62 then correspond to the pressure value thus measured by the sensor 66,to which safety values AP are added. For this, these devices 56, 60 and62 are connected to the sensor 66 by respective command lines allocatedthe references 68, 70 and 72.

By way of example, the setpoint valve for the control device 60 forcontrolling the residual nitrogen pressure corresponds to the pressure Pmeasured by the sensor 66, to which a safety value ΔP1 of between 0.1and 10 bar, preferably between 0.3 and 2 bar is added.

The setpoint value for the device 56 for controlling the oxygen pressurecorresponds to the value measured by the sensor 66, to which a safetyvalue ΔP2 of between 2 and 20 bar, preferably between 3 and 10 bar, isadded.

Finally, the setpoint value for the device 62 for controlling thepressure of the gasifier corresponds to the value measured by the sensor66, to which a safety value ΔP3 of between 0.5 and 10 bar, preferablybetween 1 and 5 bar, is added.

The three setpoint values mentioned hereinabove can therefore vary as afunction of the pressure in the delivery circuit, this pressure itselfbeing representative of the load on the turbine. It is conceivable forthese setpoint values to be varied, as a function of pressures at otherpoints of the installation. Thus, a sensor, not depicted, similar to theone 66, may be provided in the combustion chamber 8.

The invention is not restricted to the examples described and depicted.

Thus, it is conceivable to control the flow rate of just one gaseousstream, namely the nitrogen or the oxygen, using the steps describedwith reference to FIG. 1. In this case, the pressure of the othergaseous stream may be controlled in accordance with the exampledescribed with reference to FIG. 2.

It is also possible to supply the combustion chamber 8 using a singlegaseous stream originating from the air separation unit. Thus, only theresidual nitrogen produced by this air separation unit may be used, thecombustion gas being, for example, natural gas.

The invention makes it possible to achieve the aforesaid objectives.

Specifically, It has been found that the implementation according to theprior art entailed a particularly high power consumption. This is mainlydue to the fact that the nitrogen and oxygen compressors placeddownstream of the air separation unit are subject to constant setpointvalues, as concerns their output pressure which has to remain constant,and likewise the gasifier.

Now, when the gas turbine is operating at reduced capacity, the pressurein the combustion chamber is appreciably lower. As a result, in theprior art calling upon constant setpoint values, there is veryappreciable expansion of the nitrogen, of the oxygen and of thesynthesized gas in the injection valves, thus leading to considerablewastage of energy.

By contrast, varying the pressure and/or the flow rate of the oxygenand/or the nitrogen as a function of the load on the turbine makes itpossible to appreciably reduce the amount of expansion undergone bythese gases.

In particular, controlling the flow rate of these gaseous streams makesit possible to get around the pressure drops inherent in the use ofinjection valves. Indeed, according to this embodiment of the invention,the aforesaid valves can be omitted, or alternatively may have noinfluence on the implementation of the installation because they arewide open.

It will be understood that many additional changes in the details,materials, steps, and arrangement of parts, which have been hereindescribed in order to explain the nature of the invention, may be madeby those skilled in the art within the principle and scope of theinvention as expressed in the appended claims. Thus, the presentinvention is not intended to be limited to the specific embodiments inthe examples given above.

1. A method for producing energy using a gas turbine associated with anair separation unit, comprising: a) admitting air into said airseparation unit, b) extracting at least one of an oxygen stream or anitrogen stream from said air separation unit, c) compressing saidoxygen stream with a first compressor, said first compressor beinglocated downstream of said air separation unit, d) compressing saidnitrogen stream with a second compressor, said second compressor beinglocated downstream of said air separation unit, e) directing said oxygenstream toward a gasifier, f) directing said nitrogen stream toward acombustion chamber of said gas turbine, g) controlling at least oneparameter associated with at least one of said oxygen stream or saidnitrogen stream with said first compressor or said second compressor,wherein said at least one parameter is pressure, and h) assigning afirst variable setpoint value that varies as a function of a valuerepresentative of the load on the gas turbine to said at least oneparameter, wherein said value representative of the load on the turbineis a specific pressure value on the intake side of said gas turbine,wherein the pressure inside said gasifier is also controlled byassigning to it a second variable setpoint that varies as a function ofsaid pressure value.
 2. The method as claimed in claim 1, wherein saidsecond variable setpoint value is equal to said pressure increased by athird safety value.
 3. The method as claimed in claim 2, wherein saidthird safety value is between 0.5 and 10 bar.
 4. The method as claimedin claim 3, wherein said third safety value is between 1 and 5 bar. 5.An apparatus for producing energy using a gas turbine associated with anair separation unit, comprising: a) means for extracting at least one ofan oxygen stream or a nitrogen stream from said air separation unit, b)a first compression means for compressing said oxygen stream, whereinsaid first compression means is located downstream of said airseparation unit, c) a second compression means for compressing saidnitrogen stream, wherein said second compression means is locateddownstream of said air separation unit, d) means for conveying saidnitrogen stream toward a combustion chamber of said gas turbine, e)means for conveying said oxygen stream toward a gasifier, f) controlmeans for controlling at least one parameter associated with at leastone of said oxygen or nitrogen streams, wherein said control means actsdirectly on said first compression means or said second compressionmeans, and wherein said control means has a variable setpoint value thatvaries as a function of a value representative of the load on saidturbine, wherein said control means controls the pressure of said atleast one of said oxygen or nitrogen streams, and g) measurement meansfor measuring the pressure on the inlet side of the gas turbine, whereinsaid measurement means controls the pressure of said gasifier.